Reactive coarse-grain simulation for advanced material systems
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Authors
Bose, Pritom
Issue Date
2024-12
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Mechanical engineering
Alternative Title
Abstract
With advancements in computational power and algorithms, molecular dynamics (MD) simulations have become an indispensable tool in materials modeling. Well-designed simplified models, such as coarse-graining (CG) of molecular structures and using scalable potentials, enable researchers to explore larger spatial and temporal scales compared to full atomistic MD. In this thesis, we explore the utility of such models adopted very specifically for specific problems. In the first project, we set up a reactive coarse-grain simulation methodology for epoxy nanocomposite systems. In the second project, we explore the capability of a simplified hcp model to explain valuable physics. In the third and ongoing project, we implemented reactive coarse grain to prepare simulated polymer melt systems to understand the complex entanglements and their effect on the mechanical behavior. Glassy thermosetting polymers represent an important class of engineering materials known for their mechanical strength, chemical resistance, and versatility across industries. Epoxy resin, in particular, is highly valued for its exceptional adhesion, chemical and thermal stability, and electrical insulation properties, making it essential in aerospace, automotive, electronics, and structural applications. Traditional thermosetting epoxies are hard due to heavy cross-linking between the chains, however, very brittle at the same time for the same reason. Concurrent stiffening and toughening of thermosetting polymers have been a longstanding problem in material science. Experiments show that strong and stiff inclusions, such as graphene, offer some promising progress but a clear understanding of such processes is still lacking. On top of that experimental results are still mixed when it comes to simultaneously improving the stiffness and toughness of the matrix using graphene and functionalized graphene flakes. We idntified that the strength of the interface between the matrix and the filler plays an important role in determining the mechanical properties of graphene-reinforced epoxy. In this thesis, we employed reactive CG-MD to understand the effect of the interface strength on the elastic and fracture properties. We developed methodologies to model the epoxy crosslinking process using bump-LJ, a simple but reactive pairwise potential, capturing the network structure that defines their stiffness and brittleness. Reactive CG-MD enabled us to capture the brittle fracture of the epoxy resin. We identified that concurrent stiffening and toughening happens for a moderate adhesive strength between the graphene and the matrix. Both weak and strong interfaces are detrimental. Pyroelectric materials are vital in infrared sensors, thermal imaging, energy harvesting, and temperature sensing technologies. Experimental research done by our collaborators indicates that reducing film thickness enhances pyroelectric properties, making them highly effective for high-sensitivity applications. This dimensionality effect increases progressively from van der Waals (vdW) to quasi-vdW to ionic/covalent materials and is hypothesized to result from enhanced electron-phonon coupling, related to the Debye-Waller factor. In this thesis, we developed a simplified hcp structure using the bump LJ potential to simulate atomic vibrations across three material classes with varying out-of-plane bond strengths and at different thickness levels. Our findings show that Debye-Waller factor increases with reduction in membrane thickness and the enhancement is more pronounced in covalently bonded materials than in weaker vdW-bonded materials, supporting the theoretical framework and shedding light on the mechanisms driving this dimensionality effect.
Description
December 2024
School of Engineering
School of Engineering
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY